Looking for suggestions to improve acoustic coupling above 3 kHz.

Short Version:
Anybody got any suggestions as to hearing aid brand/model and earpiece form factor that can handle large gains at 3 kHz and above without feedback and is suitable for ear canals that are narrow and bend?

Long Version:
My hearing loss has worsened to the point that a cochlear implant may be in my future. However, both I and the audiologist I saw about the implant want to make sure I’ve exhausted my amplification options before going the implant route. The audiologist (who is not my hearing aid dispenser) thinks I’m currently under amplified (and I agree).

I have moderate hearing loss at low frequencies which worsens to profound at higher frequencies. An ongoing problem I have is that earpieces seem to get “leaky” somewhere in the 3 kHz to 4 kHz region. Basically, right where I desperately need all the amplification I can get, the hearing aid feedback self-test says “Nope. We’re going to squelch amplification to avoid feedback.”

Currently I’m wearing Phonak P70-R aids and I’m not getting satisfactory results from any of the dome or mould options I’ve tried. I tried the closed domes, the power domes, and c-shells. I had high hopes for the c-shells since my understanding is those should do a better job of “sealing in” the high frequencies, thereby allowing higher gains without feedback, but my hearing with those was actually worse than any of the dome options I tried.

I have narrow ear canals that bend. The narrowness makes the power domes uncomfortable (even when the “slit hack” is done) and they didn’t seem to do much better than the regular domes on the feedback test. (Actually, now that I’ve had to go to the most powerful and hence larger receiver, regardless of dome choice RITE gets uncomfortable after 4 to 6 hours). I suspect the ear canal bend(s) are what defeated the c-shells. The high frequency peformance of the c-shells was worse than the regular domes (both in terms of my subjective experience and the real ear measurement). By look and by feel it seems to me the c-shells fit more shallowly than the domes and don’t seem to have any curvature to them that would navigate the bend I’ve been told I have.

I’m looking for ideas as to what I could try next. For example, would a brand/model that offers soft material moulds be something I should look at?